1. Field of the Invention
This invention pertains to the field of shaft-mounted tools and more particularly pertains to the field of comminuting machines comprising parallel shafts rotating in opposite directions and having comminuting blades mounted thereon for shredding solid waste product.
2. Description of the Related Art
Comminuting machines that shred and pulverize various types of trash typically include two parallel, elongate shafts having a plurality of comminuting blades mounted onto, and rotating with, them. The shafts rotate in opposite directions so that trash deposited between the shafts is grabbed by the comminuting blades, pulled through, shredded, and deposited below. When the trash consists of hard objects such as metal, wood or rock, the forces generated within the comminuting machine are extremely high and cause severe loads on the comminuting blades, shafts, and mounting hardware. The severe loads lead to numerous problems in comminuting machine design: most relevant to the present invention are the loads due to longitudinal forces that tend to displace the comminuting blades along the longitudinal axes of the shafts and transverse forces that tend to bow the shafts outward. The longitudinal forces may cause the comminuting blades to move and interfere with one another reducing efficiency and blade life. To counteract the effect of the longitudinal forces it is known to preload the blades along the length of the shaft so that the blades on a given shaft are tightly compressed against one another and maintain their operating position. It is also known to counteract the transverse forces with a lateral support finger that is rigidly mounted to the frame and presses against a shaft-mounted spacer to resist lateral bowing of the shaft.
Schwarz, U.S. Pat. No. 3,845,907, discloses an apparatus for comminuting trash having oppositely-rotating parallel shafts with comminuting blades that interact. Schwarz discloses pressure rings that axially pretension the entire arrangement of blade groups on a shaft which aids in reducing the longitudinal displacement of the comminuting blades. However, it has been found that the pressure rings to not adequately prevent axial displacement of the blades when exposed to the severe loads that arise when comminuting certain types of trash product such as metal, wood and rock.
The greater of these two problems associated with comminuting machines is the transverse forces that bow the shafts. To aid in understanding the problems generated by the bowed shaft, FIG. 1 is provided which exaggerates the bowing of the shaft for purposes of illustration. FIG. 1 shows a shaft 10 and a plurality of comminuting blades 12 and spacers 14. As stated, under severe conditions there is a transverse force inducing the shaft 10 to bow. Prior art comminuting machines provided a lateral support finger 16 to resist the bowing of the shaft and also to clean pulverized trash from the spacers 14. However, it was found that the lateral support finger could not provide sufficient lateral force to resist all bowing of the shaft because of the high forces involved. When the shaft 10 bows the comminuting blades and spacers 14 fan out creating spaces 18 between the comminuting blades 12 and spacers 14. Comminuted trash infiltrates the spaces 18 which then induces significant longitudinal forces as the shaft rotates.
What is needed, then, is a means of counteracting the longitudinal and traverse forces associated with comminuting apparatus and thus prevent longitudinal movement of the comminuting blades and bowing of the shaft.